1. Field of the Invention
The present invention relates to a lighting device including a light source with a light-emitting element. The present invention also relates to a lighting device including a heat sink.
2. Description of the Related Art
A lighting device in which a light-emitting diode element (hereinafter called an LED element) functioning as a light-emitting element is used as a light source has been commercially available in recent years. Compared to a fluorescent lamp, an incandescent bulb and the like, the lighting device using an LED element consumes a smaller amount of power, provides a longer product life for a light source, and can reduce the size of the lighting device. Further, as a result of the progress of semiconductor technology, high-output and high-intensity LED elements have been manufactured at relatively low costs. Accordingly, the aforementioned lighting device is receiving attention as a light source to take the place of conventional bulbs.
Regarding the aforementioned light source with a high-output LED element, the temperature of the LED element itself is increased as the LED element itself emits light. A product life is shortened if the temperature increase of the LED element continues. Accordingly, the temperature of the LED element should be controlled, for example, by releasing heat from the LED element by connecting an aluminum plate having high heat conductivity or a metallic member such as a heat sink. In addition, an aluminum substrate or a ceramic substrate may be used as a substrate on which the LED element is to be disposed, so that heat from the LED element is transferred rapidly to the substrate, and is further released to a heat sink such as a metal plate thermally connected to the substrate.
As an example, Japanese Patent Application Laid-Open No. 2008-21505 discloses a lighting device in the form of a bulb including an LED element mounted on a flexible substrate, a substantially hemispherical cover for covering the LED element, a plurality of radially-arranged heat-releasing fins that are aluminum die-castings provided for releasing heat from the LED element, and a heat sink composed of a support body for supporting the plurality of heat-releasing fins.
In this lighting device, the support body to which the LED element is attached through the flexible substrate and the plurality of heat-releasing fins release heat efficiently through the air. Further, in this lighting device, a space is formed between the LED element and the cover (being a lens), and this space communicates with a gap between two adjacent heat-releasing fins, thereby enhancing a heat-releasing property.
However, in the aforementioned conventional technique, the following problems remain unsolved. Specifically, in the lighting device disclosed in Japanese Patent Application Laid-Open No. 2008-21505, the entire heat sink including the heat-releasing fins is provided at a position closer to a cap than a position where the LED is mounted. Accordingly, if the lighting device is attached, for example, on a wall surface so as to serve as a downlight and the like, the heat-releasing fins at a position close to the cap are covered with a reflector and the like in the form of a cup, leading to a problem in that heat cannot be released effectively. Further, while the gap between two heat-releasing fins and the space between the LED element and the cover are made to communicate with each other for heat releasing, narrowness of a communicating part makes air convection insufficient. Accordingly, most of heat inevitably remains in the space between the LED element and the cover, leading to a trouble in achieving satisfactory a heat-releasing property.